( Reaffirmed 2000 ) IS :7396 ( Part 4 ) - 19S3 Indian Standard CRITERIAFOR HYDRAULIC DESIGN OF SURGE TANKS PART Water 4 MULTIPLE Systems SURGE TANKS Committee, Conductor Sectional C[:airrnan BDC 58 P. M. MANE Consultant, ` MURAR ` 39 Shivaji Co-operative Housing Society, Pune 411016 SIUU Members Representing Bhakra Beas Management Board, Chandigarh CHIEF ENGINEER ( 13SLP ) SHRI SUDAItSIiAN KUiMAR ( Alternate) Andhra Pradesh State Electricity Board, CHIEF ENQINEER ( CIVIL ) Hyderabad SUPERINTENDING ENGINEER ( DESIGN & PLANNING ) ( A2terrzate ) Karnataka Power Corporation Ltd, Bangalore CHIEF ENIJINEEH ( CIVIL DESIGN ) SHR1 P. R. MALLIKAItJUNA ( Alternate) Public Works Department, Government of Tamil CHIEF ENUINEER ( GENERAL ) Nadu, Madras CHIEF ENGINEER ( IRRIGATION ) ( Alternate) CHIEF EIW+INEIIR ( IItRIGATION Public Works and Electricity Department, SOUTH) SUPERINTENDING+ ENGINEER ( DESIUNS ) ( Alternate) CIiIfiF EN~INEEB ( MHPD ) Government of Karnataka, Bangalore Irrigation Department, Chandi~arh Government of Punjab, DIRECTOR ( P & D ) ( Alternate ) Tamil Nadulllectricity CHIEF ENGIINEER( P & C ) SUPERINTENDING ENQ[NEER ( CIVIL ) ( Alternate) ( YAMUNA Irrigation Department, CHIEF ENGINEER Board, Madras Government ( Malabar ) of Cements Uttar .Ud, PttOJECT ) SHRI C. ETTY DARWIN DIRECTOR In Pradesh, personal Triuandrrsm Lucknow capacity 695010 Central New ) Soils and Delhi Materials Research Station, DEPUTY D~RECZ OR ( Ahernate ( Continued on page 2 ) @ Copyright 1984 INDIAN STANDARDS INSTITUTION This publication is protected under the Indian Copyright Act ( XIV of 1957 ) and reproduction in whole or in part by any means except with written permission of the publisher shall be deemed to be an infringement of copyright under the said Act. IS : 7396 ( Part 4 ) - 1983 ( Continued from page 1 ) Members DIRECTOR ( HCD-I ) DEPUTY DIRECTOR ( HCD-I DR A. K. DUBE Representing Central Water Commission, New Delhi ) ( Allernate ) Central Mining Research Station (CSIR ), Dhanbad DR J. L. JETAWA ( Alternate ) Concrete A sociation of India, Bombay SHRI N. C. DUCX+AL SHRI J. N. SUKHADWALLA ( Alternate ) Hindustan Construction Co Ltd, Bombay SHRI M. V. S. IYENoAR SHRI M. G. KHAN ( Alternate ) RESEARCH Research, Designs and Standards Organization, DIRECTOR JOINT Ministry of Railways, Lucknow ( GE-II ) National Hydroelectric Power Corporation Ltd, SHRI P. N. KHAR New Delhi National Projects Construction Corporation Ltd, SHRI A. K. MEHTA New Delhi SHRI S. C. BALI (Alternate ) Kerala State Electricity Board, Trivandrum MEB~BER ( CIVIL ) Geological Survey of India, Calcutta SHRI G. PANT SHRI N. K. MANDWAL ( Alternatt !) R. J. Shah & Co Ltd, Bombay SHRI A. R. RAICHUR General Designs Organization, Government of SRRI G. V. SATHAYE Maharashtra, Nasik Assam State Electricity Board, Shillong SRRI S. C. SEN SHRI N. K. DAS ( Alternate ) Central Electricity Authority, New Delhi DR H. R. SHARMA Himachal Pradesh State Electricity Board, Simla SERI A. K. SRIKANTIAR SHRI RANJODH SINGH (Alternate ) Director General, IS1 ( Ex-ogicio Member ) SHBI G. RAMAN, Director ( Civ Engg ) Secretary SBRI HEMANT KUMAR Assistant Director ( Civ Engg ) Panel for Surge Tanks, Convener SERI P. C. SAXENA Members BDC 58 : -P4 Representing Central Water & Power Research Station, Pune SHRI A. V. GOPALAERISRNA ( Alternate to Shri P. C. Saxena ) CHIEB ENQINEER ( CIVIL DESIGN ) Karnataka Power Corporation Ltd, Bangalore Beas Dam Project ( BBMB ), Talwara SHRI 0. P. DATTA SHRI J. S. KHURANA ( Alternate ) Institute of Hydraulics and Hydrology, Poondi, DIRECTOR Tamil Nadu Central Water Commission, New Delhi DIRECTOR ( HCD-I ) DEPUTY DIRECTOR ( HCD-I ) ( Alternate) ( Continued on page 12 ) 2 IS : 7396 ( Part 4 ) - 1983 Indian Standard CRITERIA FOR HYDRAULIC DESIGN OF SURGE TANKS PART 4 MULTIPLE SURGE TANKS 0. FOREWORD 0.1 This Indian Standard ( Part 4 ) was adopted by the Indian Standards Institution on 27 December 1983, after the draft finalized by the Water Conductor Systems Sectional Committee had been approved by the Civil Engineering Division Council. 0.2 This standard-relates to design of multiple surge tanks, provided when the water conductor system has two or more shafts, with free surface upstream of power station ( see Fig. 1 ). Multiple surge tanks occur usually in the following cases: a) The conduit conveying water from the main source to the power house may admit water enroute from other sources, for which suitable shafts ( vertical or inclined ) will be necessary. These will serve as components of multiple surge system. b) Where the head race tunnel is required to pass in the form of a syphon, a shaft may be necessary to avoid air locks. Such a shaft can form a component of multiple surge system. c) When the capacity of the existing power station is proposed to be increased and it is not possible to increase the capacity of the existing surge tank, one or more additional surge tanks at suitable economical places may be provided. requires ultimately vertical as part on consof the surge d) Sometimes construction conveniences truction shaft which can be utilized multiple surge tank system. 0.3 This standard forms part of a series of Indian tanks. Other standards in the series are as follows: IS : 7396 Criteria for hydraulic SiaG;e, Tail ( Part 1 )-1974 ( Part 2 )-1975 restricted orifice Standards design of surge tanks: and differential surge race surge tanks ( under preparation ) ( Part 3 ) Special surge tanks 3 IS : 7396 ( Part 4 ) - 1983 i+l FIG. 1 SYSTEM OF MULTIPLE SURGE TANKS AND DROP SHAFTS ( Part 4 ) lays down the criteria design of more than one surge tank on the water upstream of the turbine. 2. TERMINOLOGY 1. SCOPE 1.1 This standard for the hydraulic conductor system 2.1 For the purpose of this standard, ( Part 1 )-1974* shall apply. 3. NOTATIONS the definitions given in IS : 7396 3.1 For the purpose the meanings of this standard, indicated against each: the following notations shall have of 1, A *I> A 2 . . . . . . . . . A, n_-l' -4, n Horizontal cross sectional areas surge tanks No. 1, 2 . . . . . . n n respectively $9 At% . . . . . . . . . At,_l> An Cross-sectional areas of tunnels No. 1, 2 . . . . . . n - 1, n preceding the surge tanks respectively 4, Ath1y -%hz . . . .. . . . . Ath,_l, Thoma's areas of surge tanks No. 1, 2 . . . . . , n - 1, n respectively Lengths of tunnels No. n - 1, n respectively 1, 2 . . . . . . L,, L, r. . . . . . . . -&-.,, $9 &, Lt . . . . . . . . . L, a n-1 D, ... ... ... D n-1' &I I`t & n Lengths of tail race tunnels No. 1, 2 . . . . . . n -- 1, n respectively Equivalent diameters of tunnels No. 1, 2 . . . . . . n - 1, 71respectively Steady state initial velocities tunnels of lengths Lx, L2, L,_l, respectively Part 1 Simple, restricted orifice VO ' VfJ . . . . . . . . . y, 1 2 *Criteria for hydraulic differential surge tanks. n-1' vv,n in L, and design of surge tanks: 4 IS : 7396 ( Part 4 ) - 1983 I'l, v2 ......... vn-I, VII Velocities at any instant of time in the tunnels No. 1, 2 . . . . . . n - 1, n respectively -Y- % n2 ......... %l A,1 A, 2 Ath2 AS me-m*' Atb, ---E 4hl respectively Zl, z2 **...* . . . zn Water levels in surge tanks No. 1, 2 . . . . . . n respectively measured positive above reservoir level Discharges passing through No. 1, 2 . . . . . . respectively Discharge namely, Discharge falling into drop ith surge tank in penstocks tunnels shaft, Ql, Q2 . . . . . . . . . Q., Qd, Q2p A& A22 . . . . . . . . . As, The positive rises in water levels in surge tanks No. 1, 2 . . . . . . n respectively in short intervals of time AT AQ1, AQ2 ......... AQ, The changes in discharge in tunnels No. 1, 2 . . . . . . n respectively in short intervals of time A T Discharges through restricted orifices in surge tanks No. 1, 2 . . . . . . n respectively Co-efficients of resistance in orifices of surge tanks No. 1, 2 . . . . . . n respectively: head loss in orifice ~R = ( discharge passing through the orifice )z Areas of surge tanks No. 1, 2 . . . . _. n respectively at expansion galleries Co-efficients of hydraulic losses of tunnels No. 1, 2 . . . ,.. n respectively Ratio of total power generated by the station to that of the grid. Qh, QRI, QR,......... RI, R2 ...... ... 8, +g, Bl, p2 As2g. . . . . .. As$ . . . . . . . . . b-1, Bn El 5 IS : 7396 ( Part 4 ) - 1983 4. DATA REQUIRED 4.1 The data required for the design of simple surge tanks, as given in IS : 7396 ( Part 1 )-1974*, shall be required for this part also for each surge tank and drop shaft. the designers should ascertain whether construction shafts, drop shafts are envisaged enroute and if so their dimensions and locations should be indicated. This shall have important bearing on the design of overall surge system. 4.2 At the time of design of surge systems, 5. ANALYSIS When there are several shafts, the oscillations of each of the shafts get superimposed and interlinked in a complicated way. The influence of the nearest shaft is in general greater and therefore it is the period in relation to the nearest shaft that is more pronounced. The ratio ~between two successive maxima in any shaft is a measure of the dampening of the oscillations by the nearest shaft. 5.2 Procedure - In a system of multiple surge tanks, the continuity equation is developed at the junction of each surge tank with head race tunnel in a similar fashion as that for single surge tank [ see IS : 7396 ( Part 1 )-1974* 1. Dynamic ( equilibrium ) equation for each tunnel preceding the surge tanks is developed. In framing the dynamic equation, the surge tank preceding the tunnel acts as a reservoir, as in the case of single surge tank. A series of n number of surge tanks is shown in Fig, 1 and equations relating to this system are given in Appendix A. 5.1 General - 5.2.1 The carried analysis for tail race tunnel multiple surge tanks out on similar lines as for head race tunnel ( see Fig. 2 ). may Abe 6. DESIGN 6.1 The multiple surge tank system should be designed to withstand the worst conditions for minimum and maximum surge as specified in IS : 7396 ( Part 1 )-1974*. 6.1.1 The criterion to provide spillover in each of these shafts would be the same as specified in 6.1.1 of IS : 7396 ( Part 1 )-1974*. *Criteria for hydraulic design of surge tanks: Part surge tanks. 1 Simple, restricted orifice and differential 6 IS : 7396 ( Part 4 ) - 1983 Fro. 2 6.2 Friction 6.2.1 MULTIPLE SURGE TANKS ON TAIL RACETUNNEL Factor The formula h = f----GVNZ &4/s in metres; in metres/second; and perimeter, in metres. from 0.012 is given below: Manning's Formula - where hf = V = .W = L = 6.2.1.1 to 0.014. head loss due to friction, velocity rugosity length coefficient; of the tunnel, radius, in metres; which is area/wetted tunnels, of flow in the tunnel, R = hydraulic For concrete-lined the value of N varies 6.2.1.2 For unlined tunnels, the value of N depends on the nature of rock and the quality of trimming. Recommended values of N for various rock surface conditions are given below: Surface Characteristic Value of .N ~---~--h-_._-_ Min 0.04 0.025 0*020 ~ Max 0.06 0.035 0.030 Very rough Surface trimmed Surface trimmed and invert concreted 7 IS : 7396 ( Part 4 ) - 1983 6.2.1.3 The values of PI, Pa .., p,, may be determined from the following equations: v, 2N2L 1 = ~4/9+ other losses in the tunnel B1 v" system . .. .. . . .. ... ... ... ... ... . . . . . . , , . . . . .. . . . . . . . . . , v," N2L" Pn vn2 = 6.2.2 .&,4/3 Darcy- Weisbach Formula hf = The formula is given below: fL where /&* = friction friction 2gD f= L= v= coefiicient; Va head loss, in metres; length of the tunnel, in m; velocity of flow in the tunnel, in m/s; g= D= coefficient Pl, B2 ... acceleration due to gravity, in m/s; and diameter of the tunnel, in m. 6.2.2.1 The maxirnum, minimum and average values of friction may be taken from IS : 4880 ( Part 3 )-1976". The values of fin may be determined from the following equations: + other losses in the tunnel system + other losses in the tunnel system + other losses in the tunnel system 6.2.2.2 As the minimum coefficient gives the worst upsurge while the maximum coefficient P;ives the worst downsurge, these values shall be used for relevant conditions. In case of combination of load variations, *Code of practice for design of tunnels conveying water: Part 3 Hydraulic (first revision ) . design 8 IS : 7396 ( Part 4 ) - 1983 both the values of the coefficient sha.11 be tnkcn into account and the one which gives the worst condition shall be adopted. For calculating the worst upsurge, the maximum reservoir level should be considered whereas for the worst downsurge, the minimum reservoir level should be taken. 6.3 Area of Surge Tank - To ensure following equations shall be satisfied: n1 > As1 > where Athl is given by the following: stability 1 &Jr of the surge tank, the where HO1 the gross head measured steady state condition. from the surge tank No. 2 in the NOTE - The stability of the system is governed power house ). by the first tank ( nearest to the 6.3.1 In case there is an intermediate drop shaft enroute, the critical area of the surge tank shall be corrected to take into account the effect of additional discharge from the drop shaft as given below: where Q = Qa, = total discharge, drop shaft discharge, and analysis Li = length of tunnel from reserl oir up to the drop shaft, L = total length of tunnel from reservoir NOTE - This formula need to b? carried out. up to the surge shaft. and full stability provides only the guidelines 6.3.2 If the surge tank level of tank No. 2 is to vary over a large range, Athr may vary considerably for this range of surge tank level. In such cases, several adopted. trials shall be made to calculate Athl and the maximum &, 1 9 IS : 7396 ( Part 4 ) - 1983 6.3.3 If it can be ensured that the power station is to always operate in grid, the stabilizing effect of the grid may be taken into account and the area of surge shaft No. 1 ( ~4,~ ) may be calculated using the formula: L&r1= Athl [ 1 1.5 ( 1 -X) ] 6.4 Factor of Safety gives the minimum area. IS : 7396 ( Part 1 )-1974*. The area of the surge tank obtained from 6.3 Factor of safety shall apply as contained in 6.5 The extreme water levels in the surge tanks for the conditions enumerated in 6.1 can be determined by solving the equations given in Appendix A, preferably by computer. NOTE 1 two shafts. NOTE 2 model. Graphical method cannot be applied when there are more than It would be desirable to check the computer results in a hydraulic experiments NOTE 3 - In the case of drop shafts, however hydraulic model have to be carried out to ensure~that air does not enter into the tunnel. 6.6 Height of Surge Tanks - Provisions pertaining to the height of the shall apply to this part surge tanks given in IS : 7396 ( Part 1 )-1974* also. APPENDIX ( CONTINUITY A Clauses 5.2 and 6.5 ) FOR MULTIPLE AND DYNAMIC EQUATIONS SURGE TANK SYSTEM QLP n5! = AT AQl n'i'= QIR 5 ( 52 - 21- Lh 1QI 1&I - RI 1 QR, Qs; 121 1 QR, ) At Lll-g L&,=3 = AT *2 design of-surge tanks: Part 1 Simple, restricted orifice and *Criteria for hydraulic differential surge tanks. 10 IS : 7396 ( Part 4 ) - 1983 nrLa- AT = ( <3 - & - Pa I 9s I Qa - Rz j QR, j QR,) _fk La g . . . ..* . . . . . . . . . . . . . . . . . . . . . . . . . . . *., . . . . . . shaft. ni- NOTE- ' + A& Qi f Qa, - Qi-1 ABi ' sign to be used for drop shaft and ` - ' to be used for spilling nQ! = ( ,&+l AT . . . . . . . .. . . . . . . . . . . . . QniQs - 25 - Pi I Qi I Qi- Ri I Q!4 I Qh) 4% g . .. . .. ... . .. . .. . .. . .. A& _ AT AT 8 n -3, - Bn I Qn \Qn - Rn I nQn _ ( - QRnI Q!h 1 $- s 11 LS : 7396 ( Part ( Continuedfrom 4 ) - 1983 ) Representing Irrigation Department, Chandigarh Government Ltd, Bhopal of Punjab, page 2 Members DIRTS TOK ( PP ) SENIOR DESIQN EN~INEEE ( PP SHRI J. L. KHOSA SHRI R. P. GOEL ( Alternate ) MEMBEII. ( CIVIL ) SHRI A. K. SANDAL ) ( Alternate) Bharat Heavy Electricals Kerala State Electricity Board, Trivandrum Irrigation Department, Government of Uttar Pradesh, Lucknow Government of Maha- DR V. P. ELHENCE ( Alternate ) ENGINEER Irrigation Department, SUPERINTENDING HYDROELECZRIC rashtra, Bombay (PENCII PROJECT ) EXECUTIVE ENGINEER ( HYDRODYNAXIC DIVISION ) ( Alternate ) 12